The present invention relates to a magnetic display panel using magnetic reversal which provides clear display of records on a surface thereof and in which displayed records are erased by means of magnetism. More particularly, the invention relates to a magnetic display panel which has sealed between two opposed surface plates a liquid dispersion composed primarily of fine magnetic display grains having magnetic poles of opposite signs tinged with different colors, a dispersion medium and a fine grain thickener. In this type of panel, a desired display is recorded by the reversal of fine magnetic display grains by means of a magnetic writing instrument.
The magnetic panels proposed to date for creating displays by the use of magnetic force have been of a type in which display is accomplished by causing an external magnetic field to act upon a liquid dispersion containing medium fine magnetic grains having magnetic poles of opposite signs tinged with different colors thereby causing the fine magnetic grains affected by the magnetic field to be reversed in position and producing a record through the contrast between the pole colors of the magnetic grains so reversed and that of the magnetic grains remaining unreversed. Erasure of the display is effected by eliminating the color contrast.
Since such display devices are solely fine magnetic grains which have magnetic poles of opposite signs tinged with different colors, they have failed to produce a desired quality of display because the fine magnetic grains attract each other and coagulate and moreover because they do not produce a rotatability as required. Such display devices, therefore, have proved generally infeasible.
With a view of overcoming these difficulties by preventing the fine magnetic grains from coagulating, there has been proposed the use of fine magnetic grains possessing a low volumetric magnetization. Such fine magnetic grains, however, are deficient in being incapable of producing satisfactory rotatability. Thus, a display device using these grains is also impracticable.
There has further been proposed the use of a thixotropic liquid dispersion containing fine magnetic grains. In general, a thixotropy is a property such that when a stress is continnously applied to a liquid, the viscosity of the liquid decreases and when the stress is removed, the viscosity returns to the original value. In a magnetic display panel using such a thixotropic liquid dipersion, as the fine magnetic grains are merely dispersed in the thixotropic liquid, the rotatability of the fine magnetic grains is quite low. Further, the fine magnetic grains tend to be dispersed non-uniformly in the dispersion. As a result, a clean display cannot be obtained and it takes an excess time to record the display.
As described above, none of the conventional magnetic display panels have been able to produce clear record displays by the agency of magnetism.